Masters Degrees (Botany and Zoology)

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Browsing Masters Degrees (Botany and Zoology) by Subject "Active restoration of invaded areas"

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    Identifying priority areas for active restoration after alien plant clearing in the City of Cape Town
    (Stellenbosch : Stellenbosch University, 2016-03) Mostert, Elana; Gaertner, Mirijam; Holmes, Patricia M.; Richardson, David M.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Invasive alien plants (IAP) can have negative impacts on native ecosystems and in prolonged invasions, ecosystems can be transformed to a new alternative ecosystem state. Clearing IAP (“passive” restoration) does not always initiate native vegetation and ecosystem function recovery, therefore additional restoration measures (“active” restoration’) might be needed to set the ecosystem on the trajectory of recovery. Active restoration is more resource intensive compared to passive restoration. In some cases active restoration may be justified since, unsuccessful clearing may lead to the wasting of resources through re-invasion or secondary invasions. Restoring previously invaded or degraded vegetation can be motivated by using improved native biodiversity, ecosystem services or social benefits as incentives. To ensure the effective and efficient allocation of limited IAP control resources, some form of restoration prioritization is required. The aim of this study was thus to develop a framework to identify areas in need of active restoration and to prioritize areas for active restoration. The framework was illustrated in an urban setting by using Cape Town as a case study. In the first part of my thesis I developed two frameworks. Firstly, a framework was developed to identify areas that may need active restoration. Results of this framework are illustrated in a map indicating areas that would likely need active restoration. A second framework was developed to prioritize areas for active restoration, with a map as an outcome, indicating priority areas for active restoration. Both frameworks were built using an approach called Multi-Criteria Analysis, which is a method to construct a goal, combine stakeholder opinions and facilitate spatial restoration planning. Frameworks consisted of different criteria and sub-criteria to identify and prioritize areas for active restoration such as the extent and density of invasion, invasive species’ ecosystem impacts and conservation status of vegetation types. Criteria and sub-criteria were scored in terms of their relative importance relating to effects on vegetation recovery post-alien clearing and prioritizing areas. The framework is simple to implement and to illustrate findings and can be applied spatially and updated if new information becomes available. It can also be applied at different scales and to different ecosystems around the world; the importance of some criteria might be altered according to the ecosystem dynamics. In the second part of my thesis I conducted a field study investigating the impacts of invasions by two different types of invaders: pines and acacias; and compared their impacts on two different highly threatened lowland fynbos vegetation types. This study was also used to test the main assumptions made for the framework to identify areas for active restoration, developed in the first part of the thesis. Vegetation structure, composition and richness, and abiotic variables such as soil characteristics and litter biomass were used as criteria to determine whether ecosystems have been able to recover to a similar level than an uninvaded reference site post-clearing. Acacias changed abiotic and biotic variables after two cycles of invasion (and after one cycle of invasion in some cases) while lowland fynbos is resilient up to three rotations of pine planting. Pine-invaded areas generally had higher restoration potential than acacia-invaded areas. In terms of vegetation structure, perennial species and guild richness: acacias more negatively impacted invaded sites, whereas pine plantations recovered better in comparison to the reference site. Follow-up clearing generally promoted better ecosystem recovery in terms of overall species richness and structure but care should be taken not to damage indigenous shrubs. In conclusion, this study addressed two important aspects currently lacking in restoration, firstly by providing a framework for identifying and prioritizing areas for active restoration, to be used specifically in spatial IAP management. The two frameworks consider the multiple aspects involved in restoration, namely: biodiversity, ecosystem functioning and services, social and political aspects. Secondly, it is also a multi-species approach, considering the main woody transformers in the frameworks, testing the framework, and providing restoration recommendations for the two main lowland invaders: Pinus radiata and Acacia saligna. The overall outcomes of this study will serve as a tool for the City of Cape Town and land managers to improve active restoration efforts.